Field of the Invention
The present invention relates to a measuring apparatus. Specifically, for example, it relates to a measuring apparatus that measures a pattern by using data generated by an inspection apparatus which inspects a pattern defect by acquiring an optical image of the pattern image by laser light irradiation.
Description of Related Art
In recent years, with the advance of high integration and large capacity of a large scale integrated circuit (LSI), the line width (critical dimension) required for circuits of semiconductor elements is becoming progressively narrower. Such semiconductor elements are manufactured by exposing and transferring a pattern onto a wafer to form a circuit by means of a reduced projection exposure apparatus known as a stepper while using an original or “master” pattern (also called a mask or a reticle, and hereinafter generically referred to as a mask) with a circuit pattern formed thereon. Then, in fabricating a mask used for transferring such a fine circuit pattern onto a wafer, a pattern writing apparatus capable of writing or “drawing” fine circuit patterns by using electron beams needs to be employed. Pattern circuits may be written directly on the wafer by the pattern writing apparatus. Also, a laser beam writing apparatus that uses laser beams in place of electron beams for writing a pattern is under development.
Since LSI manufacturing requires a tremendous amount of manufacturing cost, it is crucial to improve its yield. However, as typified by a 1-gigabit DRAM (Dynamic Random Access Memory), the scale of a pattern configuring an LSI has been changing from on the order of submicrons to nanometers. One of major factors that decrease the yield of the LSI manufacturing is a pattern defect of a mask used when, by the photolithography technology, exposing and transferring a fine pattern onto a semiconductor wafer. In recent years, with miniaturization of dimensions of an LSI pattern formed on a semiconductor wafer, dimensions to be detected as a pattern defect have become extremely small. Thus, the pattern inspection apparatus which inspects a defect of a transfer mask used in manufacturing LSI needs to be highly precise.
As an inspection method, there is known a method of comparing an optical image of a pattern formed on a target object or “sample”, such as a lithography mask, imaged at a predetermined magnification by using a magnification optical system, with design data or an optical image obtained by imaging the same pattern on the target object. For example, the following is known as pattern inspection methods: the “die-to-die inspection” method that compares data of optical images of identical patterns at different positions on the same mask; and the “die-to-database inspection” method that inputs, into the inspection apparatus, writing data (design pattern data) generated by converting pattern-designed CAD data into a writing apparatus specific format to be input to the writing apparatus when a pattern is written on the mask, generates design image data (reference image) based on the input writing data, and compares the generated design image data with an optical image (serving as measurement data) obtained by imaging the pattern. According to the inspection method for use in the inspection apparatus, a target object is placed on the stage so that a light flux may scan the object by the movement of the stage in order to perform an inspection. Specifically, the target object is irradiated with a light flux from the light source by the illumination optical system. Light transmitted through the target object or reflected therefrom is focused on a sensor through the optical system. An image captured by the sensor is transmitted as measurement data to the comparison circuit. In the comparison circuit, after performing position adjustment of images, measurement data and reference data are compared with each other in accordance with an appropriate algorithm. If there is no matching between the compared data, it is determined that there exists a pattern defect.
In pattern inspection, in addition to inspecting a pattern defect (shape defect), it is also required to measure a pattern critical dimension (CD) deviation and a pattern positional deviation. Conventionally, measuring a pattern critical dimension (CD) deviation and a pattern positional deviation has been performed, separately from inspecting a pattern defect, by arranging a target object (actual mask) to be inspected in a dedicated measuring apparatus. In a pattern defect inspection apparatus, all images of a target object to be inspected and their position information are obtained and stored in order to find a defect. Therefore, if the data obtained by the pattern defect inspection can be used for measuring a pattern positional deviation and the like, a costwise and inspection timewise significant advantage can be achieved. However, conventionally, data obtained by a pattern defect inspection apparatus has been less than thoroughly utilized.
With regard to measurement of a CD deviation, there is proposed an inspection method in which a pattern line width in an image obtained for each preset region is measured, a difference from design data is calculated, and an average of all line width differences in a region is compared with a threshold value, so that a line width abnormal region is found as a CD error (dimension defect) (refer to, e.g., Japanese Patent No. 3824542).